The present invention relates to an electron beam exposure apparatus of a block exposure type, an adjusting method, and a block mask for the adjustment or, in particular, to the adjustment of a mask deflector to select a pattern of the block mask.
There is a general trend that the density of semiconductor integrated circuits increases depending on advances in micro-machining technology, and the performance required for the micro-machining technology becomes more and more severe. Particularly, in exposure technology, the limit of the optical exposure technology used for devices such as a conventional stepper has been reached. The electron beam exposure technology may be used instead of the optical exposure technology for the advanced micro-machining technology.
There are several types of the electron beam exposure apparatuses such as the variable rectangle exposure type, the block exposure type, and the multibeam exposure type. The present invention relates to the block exposure type. In the block exposure type, a repetitive figure is exposed by integrating unit patterns generated at one time by an electron beam passing through a transmission mask having unit patterns of the repetitive figure.
FIG. 1 illustrates a configuration of a beam radiation system of the block exposure type electron beam exposure apparatus. In FIG. 1, reference number 11 refers to an electron gun that generates an electron beam, 12 to a first convergent lens that forms the electron beam from the electron gun 11 into a parallel beam, 13 to an aperture that shapes the parallel beam passing through into a specified shape, 14 to a second convergent lens that converges the formed beam, 15 to a deflector for shaping, 16 to a first mask deflector, 17 to a deflector that dynamically compensates for the astigmatism of a mask, 18 to a second mask deflector, 19 to a convergent coil for a mask, 20 to a first shaping lens, 21 to a block mask moved by a stage 21A, 22 to a second shaping lens, 23 to a third mask deflector, 24 to a blanking deflector for on/off control of the beam, 25 to a fourth mask deflector, 26 to a third shaping lens, 27 to a circular aperture, 28 to a reducing lens, 29 to a focus coil, 30 to a projection lens, 31 to an electromagnetic main deflector, 32 to an electrostatic sub-deflector, and 33 to a reflected electron detector that detects an electron radiated onto a specimen and reflected thereby, and a unit that includes all the parts mentioned above is called an electronic optical lens barrel (column). The electron beam 10 from the column is radiated toward a specimen (wafer) 1 placed on the stage 2. The stage moves the wafer 1 two-dimensionally in a plane perpendicular to the electron beam 10. The electron beam exposure apparatus is further equipped with an exposure control portion that controls each portion of the column in order to expose a desired pattern.
FIG. 2 illustrates the block mask 21 mentioned above. The block mask 21 looks like a silicon substrate such as a wafer, and the block mask area where an actual aperture pattern is formed is machined by etching or the like so that the depth is about 20 xcexcm. In the block mask area, plural aperture patterns 61 are arranged in a matrix form as shown in the figure. The range in which the electron beam is deflected by the mask deflector to select the aperture pattern 61 is limited, and the size of the block mask area is determined accordingly. Each aperture pattern 61 has apertures 62 corresponding to the unit pattern of a repetitive figure. Though each aperture pattern 61 has different aperture patterns generally, plural apertures of the same shape are provided when the aperture pattern is used frequently. When a pattern is comprised of a combination of unit patterns only, it can be drawn by selecting and exposing the aperture pattern 61. Generally it is difficult, however, to form a pattern using only unit patterns, therefore, an aperture pattern 61 consisting of an entire aperture is provided so that any pattern can be drawn by shaping the electron beam that has passed using a variable rectangle method.
Moreover, plural block mask areas are provided on a block mask and the block mask area to be used can be changed by moving the block mask 21 by the stage 21A. This is because the aperture pattern may be damaged due to radiation by an electron beam over time.
To select the aperture pattern 61, the beam is deflected by the first mask deflector 16 according to the position of the aperture pattern 61 to be selected, then the beam is made parallel again with the optical axis by the second mask deflector 18, and put into the selected aperture pattern 61 perpendicularly. The beam that has passed through the selected aperture pattern 61 is deflected by the third mask deflector 23 so as to return to the optical axis, and the beam returned to the optical axis is deflected by the fourth mask deflector 25 so as to be made parallel to the optical axis. That is, the second mask deflector 18 and the third mask deflector 23 deflect the beam by the same amount but in the opposite direction as that of the first mask deflector 16, and the fourth mask deflector 25 deflects the beam by the same amount as that of the first mask deflector 16.
FIGS. 3A through 3C illustrate the size of the beam compared with the aperture pattern 61 and the influence of the deviation of the deflection position.
As shown in FIG. 3A, plural square aperture patterns 61 are arranged in a matrix form on the block mask 21. In addition to squares, rectangles may be used. The deflected beam passes through one of the plural aperture patterns 61, but a beam of large size may pass through an aperture of other proximate aperture patterns. Furthermore, an error of the deflection amount by the first mask deflector 16 may also cause the beam to pass through an aperture of other proximate aperture patterns similarly. To prevent this, the beam is made to be about the same size as the aperture pattern 61, a maximum aperture area circumscribed by a broken line is provided to the aperture pattern 61, and the aperture is formed within this maximum aperture area. This will prevent the beam from passing through an aperture of other proximate apertures as long as the deviation of the deflection position is small. For example, if the length of a side of the square aperture pattern 61 is P and that of a side of the maximum aperture area, which is arranged in the center of the aperture pattern 61, is Q, then the distance R between the side of the aperture pattern 61 and that of the maximum aperture area is (Pxe2x88x92Q)/2. As shown in FIG. 3B, the beam does not pass through an aperture of other proximate aperture patterns as long as the error of the beam position is within xc2x1R.
Since there is actually an error of the beam size, and the intensity at the edges changes gradually, it is preferable to adjust the side of the beam so as to be smaller than that of the aperture pattern 61.
As shown in FIG. 3C, however, the distribution of intensity is not uniform in the beam, and the intensity is the strongest in the center and it becomes weaker at the peripheral portion. Therefore, there exists the difference S in intensity even though the deflection position of the beam is correct and the center of the beam coincides with that of the aperture pattern 61. This difference S in intensity causes the variations in amount of exposure. Therefore, a beam with small variation is generated, and the sizes of the beam and aperture pattern, and the maximum aperture area, are determined with the variation being taken into account.
As mentioned above, due to the variation in the beam intensity, a portion of the beam with rather weak intensity may pass through the maximum aperture area of the selected aperture pattern, and the variation of the beam becomes larger after it passes through the aperture, if the position of the beam is deviated. Therefore, it is necessary to deflect the beam to the correct position of the selected aperture pattern, and to make the error in the deflection position as small as possible.
The first mask deflector 16 to select an aperture pattern of the block mask and the second through the fourth deflectors 18, 23, and 25 to cancel the deflection are generally of the electrostatic deflector type. The amount of deflection by the electrostatic deflector changes according to the voltage applied, but not in perfect proportion. Conventionally, the deflection characteristic of the first mask deflector 16 is measured and, based on the measured deflection characteristic, the voltage to be applied to the first mask deflector 16 is determined for each aperture pattern, and each deflection amount of the second through the fourth deflectors is determined accordingly. During exposure, a voltage calculated and determined according to the aperture pattern to be selected is applied.
In this manner, however, a problem in that the error is considerably large and the variation of beam intensity in the pattern is also large, when the aperture pattern is actually selected, occurs.
Conventionally, the maximum aperture area is, therefore, made relatively small compared with the aperture pattern to prevent the variation from increasing even when the beam is deviated. This measure, however, poses a limit to the size of the maximum aperture area and, therefore, to the size of a pattern to be exposed in one shot. Moreover, when the maximum aperture area is made large enough, it is necessary to enlarge the aperture pattern, resulting in the problem that the number of the aperture patterns that can be arranged in the area in which the beam can be deflected by the mask deflector, that is the number of the aperture patterns of the block mask, is reduced.
Because of the facts mentioned above, it is required to deflect a beam to the correct position using the mask deflector for each aperture pattern, and to realize this, it is also necessary to precisely measure the position of the beam deflected by the mask deflector in relation to that of each aperture pattern and, based on the measurement result, the voltage to be applied to the first mask deflector 16 for each aperture pattern should be determined, and the amounts of deflection by the second through the fourth deflectors should be also determined accordingly.
It is the purpose of the present invention to precisely determine the amount of deflection by the mask deflector for each aperture pattern by precisely measuring the relative position between the beam deflected by the mask deflector and individual aperture patterns.
To realize this purpose, according to the adjusting method of the electron beam exposure apparatus of the present invention, a block mask having at least one adjusting aperture pattern equipped with independent aperture patterns of the same shape arranged along the opposite sides of the maximum aperture area is provided, and the mask deflector is adjusted so that the intensity of the beam, which is radiated onto the specimen, at the portion of the independent apertures of the same shape arranged along the opposite sides of the adjusting aperture pattern, is uniform and maximum.
The adjusting method of the electron beam exposure apparatus of the present invention, which can be used in an electron beam exposure apparatus that has the ability to expose the patterns corresponding to the selected aperture patterns at one time, comprising an electron gun that generates an electron beam, a block mask equipped with plural aperture patterns, mask deflectors to deflect the electron beam so that it passes through one of the said plural aperture patterns selectively, and also to deflect the passed electron beam so that it returns to its original path, convergent devices that converge the electron beam that has passed through the block mask onto a specimen, and deflectors that deflect the said electron beam on the specimen, is characterized in that the mask deflector is adjusted so that the intensity of the beam, which is radiated at the specimen, at the portion of the independent apertures of the same shape arranged along the opposite sides of the adjusting aperture pattern is uniform and maximum in the electron beam exposure apparatus, wherein: the plural aperture patterns are squares or rectangles, and arranged in a matrix form; each aperture pattern has the square or rectangular maximum aperture area that limits the area in which an aperture is formed; and a block mask having at least one adjusting aperture pattern equipped with independent apertures of the same shape arranged along the opposite sides of the maximum aperture area.
The intensity of the beam which is radiated onto the specimen, at the portion of the aperture of the adjusting aperture pattern, is measured by deflecting the electron beam shaped into the adjusting aperture pattern using a deflection means and by detecting the reflected electrons when the fine lines along the sides of the maximum aperture area provided on the specimen are scanned.
When adjustment of the mask deflector is conducted for all of the adjusting aperture patterns, all of the plural aperture patterns of the block mask should be treated as the adjusting aperture patterns.
When adjustment of the mask deflector is conducted for only the aperture patterns located on the central and peripheral portions, and an interpolation is applied for other aperture patterns, a block mask on which adjusting aperture patterns are arranged only in the central and peripheral portions is used.
According to the present invention, the aperture portions of the adjusting aperture pattern correspond to the independent apertures of the same shape arranged along the opposite sides of the maximum aperture area, therefore, the variation of the beam that has passed through the maximum aperture area is the smallest when the intensity at these two apertures is adjusted to be the same.